1. Field of the Invention
The present invention relates to a method of manufacturing an insulation film, a reaction device equipped with the insulation film, a power generation device, and an electronic apparatus.
2. Related Art
In recent years, awareness for miniaturization and weight reduction of an electronic apparatus, such as a laptop computer, a cellular phone, a digital camera, or the like, have increased, and the miniaturization of the parts that are mounted in the apparatus has been required. A Micro Electro Mechanical Systems (MEMS) technique is known as a technique of producing a micro device, such as a sensor, a pump, an actuator, a motor, and a chemical reactor that are all small sized, by utilizing a silicon wafer processing technique which has been accumulated by development of semiconductor devices. For example, in the field of a reforming type fuel cell, the MEMS technique is used for a small-sized reforming type reaction device which is called a micro reactor module, in which a vaporizer, a reformer, and a carbon monoxide remover are stacked.
Each reactor (micro reactor) of the micro reactor module is constructed by forming minute grooves on substrates and then joining the substrates, on which the grooves are formed, together. The grooves are used as flow paths. Moreover, a catalyst for accelerating reactions is provided in each of the reaction flow paths. FIGS. 31A and 31B are views showing the case where the substrate is a glass substrate, and a thin-film heater combined with temperature sensor 405 and an insulation protecting layer 406 are formed on the substrate 400. FIG. 31A is a plan view of the substrate 400, and FIG. 31B is a sectional view seen from the direction indicated by the arrow with respect to the cutting plane line XXXI-XXXI of FIG. 31A. As shown in FIG. 31B, the thin-film heater combined with temperature sensor 405 composed of an adhering layer 401, a diffusion preventing layer 402, a heating resistor layer 403, and a diffusion preventing layer 404; and the insulation protecting layer 406 are formed on the surface of the substrate 400. Here, flow paths are not shown for the convenience of the drawings. The thin-film heater combined with temperature sensor bears the role of controlling the temperature of the substrate to be in a desired range, such as 280° C. to 400° C. in a steam reformer, and 100° C. to 180° C. in a carbon monoxide remover, and the role of sensing the temperature.
In a case where metal is used as the substrate, since the metal has high thermal conductivity and a small heat capacity, heat conduction from the thin-film heater, which serves as a heating element, to a supported catalyst can proceed quickly, and this provides the metal substrate an advantage of realizing effective heat utilization and high speed starting. As a metal micro reactor, one that is prepared by forming a metal oxide film by anodizing the metal substrate itself, the substrate composed of Al, Cu, stainless, or the like, and then forming a heating element on the metal oxide film, has been known (see, for example, Japanese Patent Application Laid-Open Publication No. 2004-256387). Moreover, materials capable of being anodized, such as Si, Ta, Nb, V, Bi, Y, W, Mo, Zr, and Hf, have been used as object substrates besides the metal substrate.
As mentioned above, in a case where the micro reactor is produced by using the metal substrate, since both of the substrate and the thin-film heater (combined with the temperature sensor) have electric conductivity, and a voltage is applied to the thin-film heater (combined with the temperature sensor), an insulation film is required between the metal substrate and the thin-film heater (combined with the temperature sensor). In the case of the metal micro reactor described in Japanese Patent Application Laid-Open Publication No. 2004-256387, an insulation film is provided by anodizing the substrate itself to produce an insulation film having a film thickness of 5 μm to 150 μm. However, the insulation film formed by the anodization frequently has microscopic pores, and therefore it is not expected that the insulation film has a high withstand voltage. Moreover, since the film thickness of the insulation film is thick so as to be in a range of 5 μm to 150 μm, the metal substrate also becomes thick, and thus there is a problem that the metal micro reactor is unsuitable for high speed starting, when the increase of the heat capacity of the reactor due to the thickness of the metal substrate is taken into consideration. Furthermore, since the micro reactor is operated under a high temperature environment, there is also a limitation with respect to the substrate that can be selected: a metal having a high heat resisting property (such as Ni, a Ni—Cr alloy, and an alloy including Ni such as Inconel™) must be used. Here, among rare earth elements, only Y has been cited as the object substrate.
On the other hand, in a case where a SiO2 film, which is known as a material with high withstand voltage, is formed on a metal substrate by a vapor deposition method, a sputtering method, a chemical vapor deposition (CVD) method, a coating method, or the like, the formed SiO2 film generally has an amorphous structure. As shown in FIG. 32, the SiO2 of the amorphous structure has a linear expansion coefficient in a range of 0.5 to 0.6 (×10−6/° C.), and thus is smaller than the linear expansion coefficient of a metal, which is within a range of 10 to 14 (×10−6/° C.), by two digits. Such a discrepancy between the heat expansion coefficient of the substrate and that of the film in a micro reactor, which is used under an environment higher than a room temperature, causes crack and peel-off of the insulation film when the substrate is distorted by heat, resulting in low reliability of the electrical insulation between the metal substrate and the thin-film heater (combined with the temperature sensor). Consequently, use of the SiO2 film is not preferable. In a case where high speed starting is aimed, the aforementioned problem occurs especially easily. The problem is faced not only by small reactors but is common to all the devices operating at high temperatures, such as a solid oxide fuel cell which is operated at a high temperature within a range of 600° C. to 900° C.
Here, as shown in FIG. 32, a crystal (α-quartz), which is crystallized SiO2, has linear expansion coefficients within a range of 6 to 9 (×10−6/° C.) in the a-axis direction, and within a range of 12 to 14 (×10−6/° C.) in the c-axis direction. As described above, even with the same material, linear expansion coefficients of an amorphous material and crystal material differ from each other by one digit or more. Consequently, it can be said that a crystal insulation film is suitable to be formed on a metal substrate which has a comparatively large linear expansion coefficient. However, the SiO2 film, which is a typical insulation film formed by the vapor deposition method, the sputtering method, the CVD method, the coating method, or the like, generally has an amorphous structure, and is difficult to be crystallized by an easy method such as a anneal process.
On the other hand, it is known that YOx is used as an electron emitting film of a cold cathode (see, for example, Japanese Patent Application Laid-Open Publication No. 10-269986). The crystal of YOx depends on the oxygen concentration during the oxidizing process, and five types of films are prepared. Among them, a YOx (1.32>X≧0.95) film including NaCl type is said to be suitable as the electron emitting film of the cold cathode. The method of producing a YOx film performs the steps of: forming an Y metal film on a substrate (here, the substrate includes Ni and Cr), which has been subjected to a washing process, by the vapor deposition method or the sputtering method, and then performing the oxidizing process. Subsequently, in a case where the film is a crystallite or amorphous, an anneal process is separately performed.
However, the YOx film prepared in accordance with the description of Japanese Patent Application Laid-Open Publication No. 10-269986 has an X value in a range of 1.32>X≧0.95, which is shifted from the stoichiometric value, and behaves as a good conductor with respect to an electrical property. Consequently, the YOx film has a problem that it cannot be used as an interlayer insulation film.
Accordingly, the present invention has been made in view of the circumstances mentioned above, and an object is to provide a method of manufacturing an insulation film capable of increasing the reliability of electrical isolation; and a reaction device, a power generation device, and an electronic apparatus that are equipped with the insulation film.